The present invention relates to moldable polyblends of thermoplastic polyesters blended with an ethylene copolymer containing epoxy groups, which ethylene copolymer contributes both improved impact strength and improved polymer compatibility to the blend. In particular, the present invention relates to moldable polyblends of thermoplastic polyesters and an ethylene-ethyl acrylate-glycidyl methacrylate (EEA-GMA) impact modifier having improved compatibility with polyamides and polyolefins.
Thermoplastic polyesters are a widely used class of thermoplastic molding polymers selected for their good balance of physical properties. The impact properties of these polymers can be improved by compounding with elastomeric polymer impact modifiers.
The versatility of thermoplastic polyesters has made it desirable to blend these polymers with other thermoplastic molding polymers. For example, it would be desirable to blend thermoplastic polyesters with higher-cost polyamides such as nylons to form a more economical polyblend. The polyblend would also exhibit lower moisture absorption when compared to the polyamide, thereby improving the dimensional stability of the molded parts of the polyblends. It would also be desirable to blend thermoplastic polyesters with lower-cost polyolefins such as polyethylene or polypropylene to form a highly economical polyblend possessing good impact strength and solvent resistance characteristics of the polyester.
Until now, it has not been possible to blend thermoplastic polyesters with these polymers because these polymers do not form compatible polyblends with thermoplastic polyesters. The incompatibility results in a reduction of the mechanical properties of the polyblend.
Ethylene copolymers containing epoxy groups are known impact modifiers of thermoplastic polyesters. U.S. Pat. No. 4,172,859 includes such copolymers among the thousands of suitable elastomeric impact modifiers disclosed for thermoplastic polyesters. Ethylene-methyl acrylate-glycidyl methacrylate is illustrated as an impact modifier for polybutylene terephthalate. However, none of the elastomeric impact modifiers of U.S. Pat. No. 4,172,859 are disclosed as improving the compatibility of thermoplastic polyesters with polyamides or polyolefins.
Published PCT Application 89-5,838 discloses the use of ethylene copolymers containing epoxy groups as impact modifiers for thermoplastic polyesters, but contains no disclosure regarding the impact modification of blends of thermoplastic polyesters and polyamides or polyolefins. Improvement of the impact properties of polyester molding compositions by the addition of ethylene copolymers containing epoxy groups is also disclosed in published PCT Application Publication No. WO 85/03718. This prior art reference also contains no disclosure regarding the impact modification of blends of thermoplastic polyesters and polyamides or polyolefins.
Japanese Kokai 63-113,056 discloses blends of thermoplastic polyesters and ethylene copolymers containing epoxy groups having an excellent balance of low-temperature impact strength, rubber elasticity, heat resistance, wear resistance, chemical resistance, cold strength and rigidity. However, this prior art reference also contains no disclosure regarding blends of thermoplastic polyesters and polyamides or polyolefins. Japanese Kokai 64-9,254 discloses a polyblend of polypropylene, a polyolefin, blended with an ethylene copolymer containing epoxy groups, which functions as an impact modifier to improve the low temperature impact strength and coatability of the polypropylene. There is no disclosure in this prior art reference regarding the blending of the polypropylene with thermoplastic polyesters.
U.S. Pat. No. 4,454,284 discloses blends of poly(phenylene ethers) with thermoplastic polyesters and ethylene copolymers containing epoxy groups, which improve the workability and impact strength of the poly(phenylene ether). There is no disclosure in this reference that thermoplastic polyesters and ethylene copolymers containing epoxy groups can also be blended with polyamides and polyolefins. There remains a need for multiple polyblends of thermoplastic polyesters or impact modified thermoplastic polyesters with polyamides and polyolefins.